Colorants such as pigment preparations are often produced for masterbatches. A masterbatch is an encapsulated, pelletized, or granular, dust-free concentrate of a plastomeric or elastomeric polymer comprising a fraction of a colorant. Masterbatches are used to color plastics, being added to the plastic to be colored prior to or during processing. Masterbatches are used because they provide better colorant dispersion than neat colorants and eliminate dry colorant dust from the workplace.
A variety of processes for producing masterbatches are known and the following processes are standard in the production of the masterbatches: a) the mixing of a suitable matrix (polymers) with the colorant; b) dry blending/extrusion and kneading with subsequent grinding of the colorant concentrate; or c) dry blending/extrusion and subsequent fine spraying, hot chopping, or strand pelletizing. For example, as described in U.S. Pat. No. 7,442,742, a masterbatch composition is formed from dry blending/extrusion of a colorant, a thermoplastic carrier, a metallocene polymer processing aid, and optionally an additive. In comparison to U.S. Pat. No. 7,442,742, the present invention enables up to 20% or higher loadings of active ingredients.
Split stream feeding can be utilized in extrusion processing of plastics, food products, printing toners, latex, and other materials. Split stream feeding describes the use of two or more feed streams directed to processing in an extruder.
In the production of thermoplastic laminate structures, such as in U.S. Pat. No. 4,165,210, Corbett, August 1979, plastic laminated sheet structures are produced by the combination of two streams of molten plastic and that creates a laminar flow through a die yielding a laminar sheet or tube. In U.S. Pat. No. 4,909,726, Bekele, March 1990, a coextrusion process is described in which polymer streams from multiple extruders are combined at the die of one of the extruders to form a multilayer film. In U.S. Pat. No. 5,660,922, Herridge et al., August 1997, a coextrusion process for making tapes is described in detail.
With regard to downstream feeding of temperature sensitive components in plastics and food processing, U.S. Pat. No. 4,409,165, Kim, October 1983, describes how a temperature sensitive blowing agent is introduced as a separate feed downstream of the polymer feed at a point where the polymer is compacted but not yet molten, thereby reducing the temperature at which fusion takes place. In U.S. Pat. No. 6,649,666, Read et al., November 2003, another process is described in which a feed stream of a blowing agent is introduced separately from the polymer feed stream. In the extrusion processing of foods, water is often added as a separate feed stream, typically downstream to control evaporative losses, such as described in U.S. Pat. No. 4,759,939, Keller et al., July 1988, U.S. Pat. No. 4,880,653, Keller et al., and U.S. Pat. No. 4,949,628 van Lengerich, August 1990. U.S. Pat. No. 4,965,082, Chawan et al., October 1990, describes downstream feeding of liquid ingredients in pasta production.
In the art of downstream feeding of mechanically fragile materials, such as special effects pigments and functional fillers with high aspect ratio, U.S. Pat. No. 4,495,324, Chako et al., January 1985, describes feeding short glass fibers into an extruder downstream of the polymer pellet feed into the molten polymer to make a glass fiber reinforced composite. Additional examples of downstream feeding of mechanically fragile materials include U.S. Pat. No. 5,621,040, April 1997, U.S. Pat. No. 5,723,520, March 1998, Akapeddi et al., and U.S. Pat. No. 6,776,596, Brussel, August 2004, which describe feeding long glass fibers downstream into the polymer stream, post melting, to create a high strength glass reinforced composite. As described in U.S. Pat. No. 7,488,764, Hobbs et al., February 2009, high aspect ratios are encapsulated in microspheres which are subsequently fed at the primary feed port along with polymer pellets and also downstream of the pellets into the melt. U.S. Patent Application 2011/0073799, Magni et al., March 2011, describes composites produced by downstream feeding up to 35% high aspect ratio particles that enhance thermal conductivity of the polymer.
The downstream feeding of lubricants is described in U.S. Pat. No. 4,446,090, Lovgren et al., May 1984, U.S. Pat. No. 4,877,568, Austin, May 1988, and U.S. Pat. No. 5,531,923, Le Blanc et al., July 1996, which detail feeding liquid lubricants downstream of the polymer feed into the molten polymer. U.S. Pat. No. 5,486,327, Bemis et al., describes a similar process in which liquid color concentrates, which often contain oils, are introduced downstream of the polymer to extrude a colored plastic.
Whereas, downstream feeding of liquid components to adjust the viscosity of a material is described in U.S. Pat. No. 5,316,578, Buehler et al., May 1994, and U.S. Pat. No. 5,480,923, Schmid et al., January 1996, with regard to extrusion processing of starch products and the introduction of liquids downstream to reduce product viscosity in a controlled fashion.
The downstream feeding of particulate additives and fillers is described in patent literature with regard to particulate functional additives and fillers in the production of plastics materials. U.S. Pat. No. 4,906,421, Plamthottam, January 1990, describes downstream feeding of fillers, U.S. Pat. No. 5,969,089, October 1999, describes adding fillers and functional additives downstream of resins, and U.S. Pat. No. 6,242,127, June 2001, describes downstream addition of functional additives in a film extrusion process.
Downstream feeding of flame retardant additives is described in U.S. Pat. No. 6,713,598, Selvaraj et al., March 2004, U.S. Pat. No. 6,800,677, Yakobe, October 2004, which also includes downstream feeding of glass fibers for reinforcement, and U.S. Pat. No. 7,939,585, Gaggar et al., May 2011.
U.S. Pat. No. 6,287,692, Luo et al., September 2001, describes extrusion processing of wire and cable compounds in which particulate additives are introduced downstream of the polymer feed.
U.S. Pat. No. 8,367,755 describes polyphenylene ether thermoplastic compounds for sheet extrusion and molding in which additives are introduced downstream of the polymer feed during extrusion processing to make the compounds.
The use of split resin streams in the production of polymer alloys and blends via extrusion processing is described in U.S. Pat. No. 4,547,541, Golba, October 1985, U.S. Pat. No. 5,225,488, Baird et al., July 1993, U.S. Pat. No. 5,420,198, Papazoglou et al., May 1995, U.S. Pat. No. 7,182,886, Elkovitch et al., February 2007, U.S. Pat. No. 7,868,090, Ellul et al., January 2011, and U.S. Pat. No. 8,148,466, Wood et al., April, 2012.
Split stream feeding in reactive extrusion processes is known and described in U.S. Pat. No. 7,148,314, Gallucci et al., December 2006, which details feeding of a component with a desired functional group downstream of a polymer to then react with it and yield a functionalized polymer, and U.S. Pat. No. 7,829,640, Barbieri et al., November 2010, which details an extrusion reaction process in which the output stream is fed back to the feed throat for further reaction.
Adding a colorant feed downstream of the resin feed is described in U.S. Pat. No. 6,352,654, Silvy et al., March 2002, and U.S. Pat. No. 6,776,929, Hossen, August 2004, with regard to the production of an electrically conductive polymer via extrusion processing in which conductive carbon black powders or masterbatches are introduced downstream of the polymer feed into the melt.
Utilization extrusion processing in which a molten polymer is fed as a second feed stream has been described in U.S. Pat. No. 5,376,702, Stibel et al., December 1994, wherein a secondary polymer stream is split off, combined with other components, and then recombined with the primary polymer stream. In U.S. Pat. No. 6,010,723, Song et al., January 2000, a process is described for making chewing gum in which components of the recipe are compounded in a first extruder which then feeds its output to a second extruder into which are also fed components that will reduce the viscosity of the melt stream from extruder 1.
Extrusion compounding of a complex mixture of particulates, liquids, and resins in which a binder is fed downstream has been discussed in U.S. Pat. No. 4,894,308, Mahabadi et al., January 1990, wherein extrusion processing of electrostatic dry printing toners occurs by utilizing a dry blend of surfactants and pigments at the main feed port, which are melted under heat and pressure, and then conveyed past a second feed port where a polymer is introduced as a powder or pellets. U.S. Pat. No. 7,572,567, Chung et al., August 2009, describes a process in which an aqueous solution of poly Aluminum Chloride is introduced downstream as a coagulating binder into the melt stream of pigments and other components of an electrostatic toner for dry printing.
The described art is related to materials that were intended to be fabricated into parts or materials and methods for fabricating constructions. In contrast, the present invention relates to a process and materials for making an intermediate that is used to color thermoplastic materials; specifically, color and additive masterbatches.
In Stibel et al. (U.S. Pat. No. 5,376,702, December 1994), a separate molten polymer stream is combined with additives, and then recombined with a primary feed. In contrast, the present invention describes the counter-intuitive process of premelting the majority of the resin component of a masterbatch formulation which serves as the carrier or binder to increase the density to (i) create additional free volume in the feed throat for adding colorants and additives and (ii) start the pigment wetting process immediately upon contact with the resin.
Song et al. (U.S. Pat. No. 6,010,723, January 2000 and earlier patents) describes feeding the output of an extruder into the primary feed of a second extruder for the purpose of introducing viscosity reducing additives via the second extruder. Whereas, in the present invention, the majority of the resin component of a masterbatch formulation is pre-melted, and serves as the carrier or binder to densify the formulation to (i) create additional free volume in the feed throat for adding colorants and additives and (ii) begin the pigment wetting process immediately upon contact with the resin.
The invention also differs from Corbett, U.S. Pat. No. 4,165,210, August 1979, which describes the concept of bringing streams of molten plastic together in a die to form laminate structures. Similar differences exist between the current invention and the coextrusion processes described by Bekele, U.S. Pat. No. 4,909,726, March 1990, and Herridge et al., U.S. Pat. No. 5,660,922, August 1997.
The concept of adding pigments downstream of a resin feed is known. For example, U.S. Pat. No. 6,352,654, Silvy et al., March 2002, and U.S. Pat. No. 6,776,929, Hossen, August 2004, describe production of an electrically conductive polymer via extrusion processing in which conductive carbon black powders or masterbatches are introduced downstream of the polymer feed into the melt, where the carbon black is a minor component of the total composition. However, the invention relates to the downstream addition of pigments comprising up to 80% of the total composition.
Various patents describe downstream feeding of fillers, such as short glass fibers and composites with up to 70% glass fiber, which are commercially available. Colorants, however, have a much higher surface area to wet out, and as noted above, are dosed in as minor components downstream.
The prior art fails to describe introducing a pre-melted resin carrier feed downstream of the powder feed. Nor does it describe the concept of pre-melting the resin feed for the combined purposes of increasing the volume available for the powders to achieve higher loading than previously possible and initiating the wetting out process on contact. The invention described herein provides a volume enhancement in the primary feed in which the polymer melt feed and the colorant mix feed are introduced at the same primary feed throat. Furthermore, none of the patents described relate to the introduction of the polymer feed as a molten stream that is the output of a second melt processing unit, or relate to feeding the resin stream is upstream of the colorant mix feed. The methods cited in the prior art describe an extrusion process in which the resin is compressed and melted in the extruder prior to reaching the zone where the downstream feed port is located. However, as described in detail herein, there are advantages in pre-melting the resin in a separate device: (i) the compression, kneading, and melting zones of the primary extruder can be minimized; (ii) the process is more energy efficient in that more of the energy supplied to the extruder is used to affect incorporation and dispersion of the colorants and additives, enabling higher production rates, and (iii) a simple single screw extruder or melt pump can be used to pre-melt the polymer. Based on this, the total cost of the combined system can be lower than or comparable to that of the conventional extruder alone.
Known masterbatches formed from dry blending/extrusion are generally formulated using a method which includes a thermoplastic polymer, a colorant, a dispersant, and optionally one or more additives. The thermoplastic polymer is commonly referred to as a “carrier” or “carrier resin.” A typical commercial formulation of a masterbatch, particularly formulated with a mixture of colorants (pigments and dyes) includes about 30% by weight of colorant, about 5% by weight of dispersant, about 10% by weight of additive, and about 55% by weight of a carrier.
Unfortunately, known masterbatches formed from dry blending/extrusion, particularly those comprised of blends of colorants (pigments and dyes) have a relatively low colorant concentration. Thus, it has been found that many known masterbatches introduce unnecessary costs and undesired amounts of auxiliary ingredients, such as carrier matrix. Particularly in the case of colorant formulations containing relatively high proportions of organic pigments, higher loadings of colorant cannot be used in known masterbatches produced from dry pigments due to insufficient dispersion. Insufficient dispersion of the colorant particles can lead to a decrease in physical and mechanical properties of the end product, such as tensile strength, flexural modulus, elongation, and impact strength. Also, pigment agglomerates can lead to surface imperfections that affect the part's appearance.
Organic pigment dispersion in conventionally produced masterbatches can be improved by using mostly or entirely powdered or finely granulated resins. However, this practice results in introducing dry blend mixtures of resin, colorants, and other ingredients having a significantly lower bulk density than mixtures with resin pellets. Less material is introduced into the extruder in any given time, resulting in a significant reduction in processing rate.
Another deficiency in known dry blending/extrusion masterbatch compositions is the inability to significantly improve the processability of the masterbatch itself and the end product.
Another deficiency in known dry blending/extrusion masterbatch processing is the blend volume limitation in the feed throat of an extruder. Fixed volume in the feed throat limits pigment and additive loadings, particularly in the case of organic pigments and certain effects pigments, such as pearlescent pigments, due to the low bulk density of these pigments. Similarly, these limitations on the amount of material introduced at the feed throat significantly reduce extrusion throughput and color strength.
Problems due to the fixed volume in the feed throat could be alleviated by increasing the free volume in the feed throat by using thinner flights, adding deeper roots on the screw, and extending the length of the opening; however, all of these attempts will only provide small incremental gains in the volume space (e.g., 10-15% more free volume space), do not provide the desired increase in pigment and additive loading, and sacrifice the strength and life of the screw.
Another deficiency in known dry blending/extrusion masterbatch compositions is the inability to include relatively significant amounts of loading with regard to additives such as ultraviolet light absorbers, light stabilizers, antioxidants, and blowing agents. Generally, additives are added only if desired and then in small amounts. Otherwise, it is believed that the processability of the masterbatch would be impaired.
In addition, other deficiencies in processing known dry blending/extrusion masterbatch compositions are inefficiencies of the work provided by the extruder and inefficiencies of the length of the extrusion cycle. Specifically, much of the energy and residence time is spent melting the polymer carrier instead of dispersing colorants.
Presently, there is no known system or method for providing a masterbatch composition that avoids the foregoing problems associated with conventional masterbatches. Accordingly, it is desirable to provide a masterbatch composition with improved processability that increases loading of the masterbatch composition as well as the coloration of the end product without sacrificing production rate, production throughput, physical and mechanical properties of the colored parts, and surface appearance, all the while introducing less carrier resin into the end part.
The present application, as described and claimed herein, addresses the above described deficiencies of prior art masterbatches and processes for developing the same.